It is well known that a thin metal film can convert microwave energy into thermal energy for heating a variety of food products. One prevalent use of such material is in the microwave popping of corn.
Such thin metal film, usually aluminum, is provided on a support which is a polymeric film and discrete patches of such thin metal film generally are provided thereon by selective demetallizing of a metallized polymeric sheet, such as by using any of the procedures described in U.S. Pat. Nos. 4,398,994, 4,552,614 and 4,610,755, the disclosures of which are incorporated herein by reference.
When microwave energy is applied to the metal film supported by the polymeric substrate, distortion occurs and the metal film becomes ineffective. It is necessary, therefore, to laminate the plastic film to a suitable non-conductive, heat-stable layer to prevent such distortion from occurring during application of microwave energy.
A search conducted in the facilities of the United States Patent and Trademark Office with respect to this invention has revealed the following prior art:
3,984,598 Sarazin PA1 4,592,914 Kuchenbecker PA1 4,641,005 Seiferth PA1 4,661,671 Maroszek PA1 4,676,857 Scharr et al. PA1 4,702,963 Phillips et al. PA1 4,703,148 Mikulski et al. PA1 4,716,061 Winter
In addition, the applicant is aware of U.S. Pat. Nos. 3,235,395 and 4,349,402.
U.S. Pat. Nos. 3,325,395 and 4,349,402 describe metal transfer processes for applying metallic coatings to a variety of substrates, including paper, for the purpose of providing a shiny coating. These references are silent as to any potential application to microwave energy converting their metallic films.
U.S. Pat. No. 3,984,598 describes the production of metal-clad laminates for use in electrical components. Again, no reference is made to any potential application to microwave susceptor films.
U.S. Pat. Nos. 4,592,914, 4,641,005, 4,661,671, 4,702,963, 4,703,148 and 4,716,061 describe a variety of food containers having a layer of microwave susceptor material incorporated into the structure. No mention is made of the employment of a transfer process in the formation of the microwave heat susceptor layer.
U.S. Pat. No. 4,676,857 describes a method of making microwave heating material. In the procedure described in that patent, a pre-selected metallized pattern is disposed on a layer of dielectric material using a hot stamping transfer process in conjunction with aluminum roll leaf. The metal employed is of a thickness that enables microwave energy incident thereon to be converted to thermal energy.